JavaScript one-liner function: parseQuery and buildQuery (>=ES2017)

parseQuery_buildQuery.js

// for ES2017
{
  // "name=matsuby&age=27" => {name: "matsuby", age: "27"}
  const parseQuery = qs => typeof qs!=="string"?{}:Object.assign({},...Object.entries([...new URLSearchParams(qs)].reduce((a,c)=>Object.assign(a,{[c[0]]:a[c[0]]?[...a[c[0]],c[1]]:[c[1]]}),{})).map(e=>({[e[0]]:e[1].join(",")})));
  
  // {name: "matsuby", age: "27"} => "name=matsuby&age=27"
  const buildQuery = qo => new URLSearchParams(Object.entries(qo).map(kv=>kv[1].split(",").map(v=>[kv[0],v])).reduce((a,c)=>a.concat(c),[])).toString();
  

  const testParams = [
    // expect:
    //   parse: query object
    //   build: query string
    "name=matsuby&age=27",     // standard
    "?name=matsuby&age=27",    // ignore first "?"
    "name=matsuby&age=27&",    // ignore last "&"
    "?name=matsuby&age=27&",   // ignore first "?" and ignore last "&"
    "name=matsuby&name=john",  // not unique => concat value string with ","(csv string)
    "name=",                   // key only, value is empty string("")
    "name",                    // key only, value is empty string("")
    "?%E3%81%82=%E3%81%84",    // decode uri
    location.search,           // browsing page test

    // expect:
    //   parse: empty object({})
    //   build: empty string("")
    "", 0, 1, true, false, null, undefined, NaN, [], {},
  ];

  for (p of testParams) {
    const t = p !== p ? p : JSON.stringify(p);
    const pq = JSON.stringify(parseQuery(p));
    const bq = JSON.stringify(buildQuery(parseQuery(p)));
    console.log(`${t}: ${pq} => ${bq}`);
  }
}